Megatron Electrostatic Headphone Amplifier

[nopants]

2sa1967 should work as well, it's just not insulated

[mypasswordis]

Interesting, where do I get those? Bdent also has them for $9 and I see some guy on HF might be selling some.

 

Meanwhile good old Dalbani is selling 1968s for $112.

[kevin gilmore]

dalbani guaranteed to be the fakes that birgir and I returned.

 

2sa1486 works, just flip it around.

 

stn9360 works if you make (or someone makes) the little adapter board

[spritzer]

Anything on ebay would be fake too.  Hell most of them have sanding marks and with 2SA1968 laser etched afterwards, not even close to how the original looks. 

 

After helping some users with their Megatron I have some ideas on how to improve the PCB and make it more user friendly.  Swapping to the STN9360 for the CCS would make sense. 

[mypasswordis]

Thanks, after the whole Dalbani fiasco it's not like anything else should be expected. I just find it funny that they're charging $112 for a fake part, at least the Ebay scammers are more modest.

 

I was thinking of running the front end at 400V (more like 390V, but we'll see how close I can get with the zener references in the PS), which would be pushing the limits for sure with just a single part. Stacking also helps split the power dissipation for the small SOT223 package. Maybe I'll think up a clever way to put in a dropping resistor on the positive rail so I don't have to bother with all of that; suggestions are welcome. All CCSes will be on separate protoboards since I am building from the BATE PCB. I bought adapter boards here, they're super cheap and even come with 90 degree header pins: http://www.ebay.com/itm/271302222232?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Edited March 22, 2014 by mypasswordis

[spritzer]

There is nothing to be gained from running the front end at 400V, well nothing but bad things that is.  There is already a dropping resistor on the board for just this setup. 

 

Those adapters are cool but there seems to be very little in the way of heatsinking.  Shouldn't be a problem but something to look out for...

[nopants]

I would suggest that you mount the LEDs with the same orientation as the tube sockets, it makes things easier to troubleshoot after assembly/during powerup. One of mine was bad and it was impossible to see

[niner]

Got a question on the schematic vs PCB.  In the schematic, the anodes of two 12V Zener are tied together.  But on the PCB, both cathodes are tied together instead.  Which one is right?

[kevin gilmore]

same thing, just a voltage protector.

[niner]

Thanks.

[nopants]

in preparation for California's hot spring and summer, I finally got around to bringing in the megatron to work:

I'm pretty sure this looks imposing enough that I won't have to worry about anyone stealing it. Modified Lavry underneath the laptop

[niner]

To the fellow green tea drinker.  Nice!  It will be even better if you add a sign of "Danger, High Voltage"

 

I hope to power up the my Megatron this coming weekend.  Need to finish up the power supply board first.

[nopants]

Can anyone comment on using Antek transformers for a Megatron/KGST build? I'm trying to reduce my dependency on SumR custom products, and edcor seems to have leadtimes for all the relevant transformers.

 

Antek seems to provide a number of transformers with both HV and filaments on a single toroid- are there any problems with using those filament windings on the output? 

[niner]

I'm using the Antek 400VA 430V transform in my KGSSHV build.  It is temporary until SumR finished my transformer.  In this particular application, the transformer is always quiet and cool.  I didn't use the filament windings.

 

This weekend, I will bring up my Megatron build with this transformer (again, waiting for SumR for the proper one).  I'll let you know how it goes.

[n3rdling]

I also got the Antek.  I trust them more than sumr, the price is good, and there's no wait

[spritzer]

Can't go wrong with Antek.  Dirt cheap and very well made. 

[dsavitsk]

Can't go wrong with Antek.  Dirt cheap and very well made. 

 

I'll agree with the dirt cheap part. Just make sure you measure the secondaries to be sure they do what you think they are doing.

[spritzer]

Yeah, always better to do that.  Though with a KGSSHV psu it is almost impossible to overload the input... 

[eggil]

Well, Antek is sold out on the following 25va, 2 x 6.3v:

http://www.antekinc.com/an-0206-25va-6v-transformer/

They do have this one though, 50va, 2 x 6.3v

http://www.antekinc.com/as-0506-50va-6v-transformer/

SumR has these 30va, 2 x 6.3v:

http://www.sumr.com/universal/30va_universal.htm 

Edited April 19, 2014 by eggil

[spritzer]

Mouser has some nice filament transformers too.  Dirt cheap...

[eggil]

Well, my PSU powered up without a hitch: +456V,  -452V; +15.15V, -14.86V

Will test the amplifier in next few days. Don't have the 6Ca7's yet and missing one small transformer.

For me, the most difficult part is always the casing.

Never mind the dirty filter

The transformer is SumR

Edited May 14, 2014 by eggil

[nopants]

I would switch those LEDs to the other side of the board if you can hack it, one of mine was broken and it was very difficult to troubleshoot from a first glance

[eggil]

So you made holes on the top panels for the LED's?

Time to use my Hakko 808 

[nopants]

no more like I left them on the underside and never made a top panel, I made the poverty-case version

 

Meagertron?

[eggil]

Moved the LED's to the other side.

And playing with my new Macro lens and camera